1. Field of the Invention
The present invention relates to pressure sensors and other sensors for measuring a fluid pressure.
2. Description of Related Art
For measurement of fluid pressures, pressure sensors are used. One of such pressure sensors includes: a joint provided with a port for introducing a target fluid; and a sensor module provided on the joint and having a diaphragm displaceable by a pressure of the introduced fluid, and converts the displacement of the diaphragm into signals for outputting.
As such a pressure sensor, Traditional Example 1 is known, according to which the sensor module is accommodated within a case and a circuit board is positioned on the sensor module (Document 1: JP-A-11-148880). In Traditional Example 1, the circuit board is held in a resin holder and connected to a connector via a connecting pin, so that the signals generated in the circuit board are outputted to the outside from the connector.
Further, as pressure sensors having sensor modules, Traditional Examples 2 and 3 are known, according to which a first end of a flexible circuit board is connected to the sensor module and a second end of the flexible circuit board is connected to the circuit board (Document 2: JP-A-2008-241343, Document 3: JP-A-2008-224512).
In Traditional Examples 2 and 3, the diaphragm of the sensor module is provided with a cap, so that the first end of the flexible circuit board is wired around the cap. The second end of the flexible circuit board is connected to a circuit board spaced away from the sensor module. Electronic components are provided on the upper surface of the circuit board.
Still further, as pressure sensors having sensor modules, Traditional Examples 4 and 5 are known. According to these examples, a bottom of a bottomed cylindrical case is attached to the joint while a circuit board is provided at an open-end side of the case, and electric circuit components are provided on the circuit board so as to oppose to a diaphragm of the sensor module (Document 4: JP-A-11-201852, Document 5: JP-A-11-237291)
In Traditional Examples 4 and 5, the bottom of the case contacts the joint, and this bottom is provided with an opening for allowing an insertion of the sensor module. The opening of the bottom is provided with an engaging projection for positioning the case on the joint, and the outer circumference of the engaging projection is locked with a wall of a groove formed in the joint.
Traditional Example 1 employs a layer structure in which the circuit board is positioned on the sensor module and the connector is positioned on the circuit board via the connecting pin. With this structure, a height dimension of the sensor (height from the sensor module to the connector) is increased, which invites increase in the size of the pressure sensor.
Traditional Examples 2 and 3 employ structures in which the cap is provided on the sensor module, the circuit board is positioned away from the cap and the flexible circuit board is positioned between the circuit board the cap. With this structure, as in Traditional Example 1, a dimension from the sensor module to the circuit board is increased, which invites increase in the size of the pressure sensor. Moreover, the above structures require a separate circuit board for mounting electronic components in addition to the flexible circuit board, which invites increase in manufacturing cost.
Traditional Examples 4 and 5 employ layer structures in which the circuit board is provided on the sensor module and the electric circuit components are provided on the circuit board to oppose to the sensor module, so that the height dimension of the sensor is increased. In this respect, according to Traditional Examples 4 and 5, the joint is provided with the groove, and the engaging projection of the case is engaged with the groove. However, the groove and the engaging projection are for positioning, and thus the height dimension of the sensor is increased all the same.
Further, Traditional Examples 4 and 5 require the case to have a complicated shape, according to which the bottom of the case is open and the opening portion is provided with the engaging projection for positioning the case on the joint. Hence, the structure of the case per se becomes complicated, which invites increase in manufacturing cost.